The present invention relates to a liquid filter assembly and, more particularly, to unique vented filter assemblies which purge air therefrom in the filtering of parenteral and other liquids during the administration thereof.
For some time it has been the preferred practice to filter intravenous and other parenteral solutions prior to the administration of such solutions to a patient to remove particulate matter that may be present in the solutions. Many different filter structures have been utilized for this purpose and many different procedures have been devised to insure that the liquids are properly filtered and administered with the highest degree of safety for the patient.
Recently, filter media have become commercially available that permit the filtration of intravenous liquids down to a particle size of about 0.22 microns. This is significant in that a filter having this pore size effectively serves as a bacteria retentive screen and filters out all bacteria from the liquids in addition to removing particulate matter. Heretofore, one of the main drawbacks of utilizing a 0.22 micron filter was that a very high pressure drop was created by the presence of the filter, thus, necessitating the use of a pump to sufficiently overcome the back pressure. Also, the 0.22 micron membrane filter media that have been found to be particularly applicable for use in the filtering of intravenous liquids are exceptionally difficult to handle during the fabrication of the filter media into appropriate filter structures. This is true because most of such filter media have very low tear strengths and do not form adequate heat seals with other plastic materials. Therefore, the geometrical configurations heretofore available with the 0.22 micron membrane filter media have been relatively flat surfaces which greatly limit, because of size considerations, the available filter area for the passage of liquids. Thus, the problem of excessive back pressure is increased because of the relatively small filtering surfaces.
Another significant problem encountered in the use of prior filters was that of air blockage due to improper priming. Since the type of liquid filters contemplated by this invention have hydrophilic properties, they do not pass air and, consequently, air accumulates at the filter surface and reduces the available filtration area. The result of this air accumulation at the filter surface is that it reduces the flow rate and contributes to the malfunction of the system. A significant portion of this problem may be overcome by priming the filter assembly prior to its use; however, since prior filters have been constructed from relatively rigid housing materials, this priming technique has been relatively complicated and has not always been effective in removing all of the air from the filter housing.
One of the ways to prime the filter has been to separate the filter assembly itself from the intravenous tubing so that air can escape from the filter. This, of course, requires the attendant to not only observe the intravenous flow for air blockage of the filter, but also to interrupt the intravenous feeding procedure to purge the air which is causing a blockage. As air enters the intravenous line due to a number of causes, it becomes necessary to constantly monitor the flow since the air does not purge itself, but requires some action on the part of the attendant or clinician.
A filter adapted to separate gases and liquids while performing the filtration function is disclosed in U.S. Pat. No. 3,854,907. A non-wetting filter material allows gases inside the filter cover to be vented through a relatively long tubular cylinder and to be conducted to an outlet port in the bottom of the filter cover. This structure represents one way in which undesirable gas or air entering into a fluid filter assembly with fluid may be removed. Thus, there is room for further improvements in simplicity of structure, cost of manufacture, convenience of use and handling, and in performance and specific functions of a vented filter assembly.